Chloroform extracts of many tropical and sub-tropical blue-green algae, notably in the Oscillatoriaceae, and some brown and green seaweeds exhibit good activity against P-388 leukemia or Ehrlich ascites tumor in mice. Isolation of the anticancer compounds will be carried out using either P-388 or Ehrlich ascites bioassays in our laboratory to monitor the fractionations. Molecular structures will be elucidated by a combination of hydrolytic, oxidative, and reductive degradations and physical methods, including optical, magnetic, and mass spectrometry and when feasible X-ray crystallography. The pure anticancer compounds as well as derivatives will be sent to NCI laboratories for chemotherapeutic evaluations.